Communication systems typically include a plurality of dispatch consoles and communication units, such as mobile or portable radio units, that are geographically distributed among various base sites and dispatch sites. The communication units wirelessly communicate with the base sites and each other, and are often logically divided into various talkgroups. Communication systems may be organized as trunked systems, where a plurality of radio frequency (RF) communication resources are allocated amongst multiple users or groups by assigning the base sites and RF channels within a coverage area on a call-by-call basis, or as conventional (non-trunked) systems where RF communication resources are dedicated to one or more users or groups. In trunked systems, or in mixed trunked and conventional systems, there is usually provided a central controller/server (sometimes called a “zone controller”) for allocating RF communication resources among a group of sites. The zone controller may reside within a single device or multiple devices and may be located at a fixed equipment site or may be distributed among the base sites.
Calls among the communication units are typically of the dispatch type, or better known as push-to-talk (PTT). Each time a communication unit is keyed to begin a call, the call is assigned to an available wireless channel. The originating communication unit begins transmitting on the assigned channel and continues to transmit on the assigned channel until the communication unit has been dekeyed by the user. Other communication units in an associated talkgroup also switch to the assigned channel and begin listening to the call.
In current communication systems where communication units operate in a half-duplex mode, a transmitting communication unit is not capable of receiving any signals or commands from a base site while it is transmitting. This often results in a problem if there is a need to stop a communication unit from transmitting before it has dekeyed. For example, if a dispatch operator needs to transmit an urgent call, there is no way to signal the transmitting communication unit to stop transmitting and listen to the call from the dispatch site. Similarly, if another communication unit needs to transmit an emergency call on this particular channel, the emergency call either has to be postponed until the originating communication unit has dekeyed or transmitted simultaneously with the call from the originating communication unit. The former results in an undesired delay in transmitting the emergency call while the latter often results in significant interference between the two calls.
Accordingly, there is a need for a system and method for interrupting a transmitting half-duplex communication unit during the transmission of a call.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions and/or relative positioning of some of the elements in the figures may be exaggerated relative to other elements to help improve the understanding of various embodiments of the present disclosure. Also, common but well-understood elements that are useful or necessary in a commercially feasible embodiment are not often depicted in order to facilitate a less obstructed view of these various embodiments of the present disclosure. It will be further appreciated that certain actions and/or steps may be described or depicted in a particular order of occurrence while those skilled in the art will understand that such specificity with respect to sequence is not actually required. It will also be understood that the terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meaning have otherwise been set forth herein.